Perforated pipe structure



Feb 10, 1959 D. w. FETHER PERFORATED PIPE: STRUCTURE Filed sept@ 6, 1955 FIG. lZ.

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United States Patent O PERFORATED PIPE STRUCTURE Donald W. Fether, Encino, Calif.

Application September 6, 1955, Serial No. 532,442

6 Claims. (Cl. 11M-235) This invention relates to well pipe structures of the type used in oil wells, and is particularly useful as a perforated formations.

Perforated pipes have been used for many years in oil wells to screen out sand and other foreign matter while permitting the well iluid to enter the liow pipe in the well. A pump is commonly placed in the well to receive the liuid entering the well pipe through the perforations and to pump the oil to the surface through the tubing. It is known that a large number of the perforations in the pipe are plugged up as the pipe is lowered into position. This occurs because the well bore is not absolutely straight and consequently the perforated pipe scrapes on the sides of the bore as it is lowered into place. The well surface of the well bore commonly is coated with mud cake which is left as a deposit from the circulating mud fluid used in the drilling of the well. This mud cake scrapes off readily and fills up the perforations so that many of them do not function at all.

It is known that perforated well pipes have been sheared otr` laterally in the hole after a period of use and it is believed that this occurs when many of the perforations on one side of the pipe have become plugged so that well fluid enters only through perforations on one side of the pipe only. The increased velocity of the well iiuid which develops as a result of lack of suiiicient perforations causes excessive erosion of the formation on one side of the well pipe. Mud cake and rock formation parts falling into the well bore around the perforated pipe from higher locations in the well form a relatively solid pack around the perforated pipe on the side where the perforations are plugged. Radial pressure from the accumulation of this material serves as a wedge to move the perforated pipe into the eroded pocket adjacent the active perforations. Eventually, the wedging force becomes sufciently great to collapse the perforated pipe and even to shear it olf laterally.

In certain types of wells where the formation contains considerable gas dissolved in the well iiuid, diiculty is encountered in operating the pump efficiently because of foaming which occurs at the active perforations. The foaming is believed to result from the momentary high velocity of the well liud as it enters an active perforation `in the pipe; the increase in velocity is accompanied by a decrease in pressure with the result that gases come out of solution to produce a foam and this foam interferes with the proper operation of the pump.

It is the principal object of my invention to provide a new and improved form of well pipe structure which has markedly increased resistance to lateral crushing, and without requiring pipe of excessive wall thickness.

Another object is to provide an improved perforated pipe structure which includes means for trowelling the walls of the well bore to prevent plugging of the perforations when the device is being lowered into the hole.

Another object is to provide an improved perforated pipe structure which functions to minimize objectionable foaming action.

. liner through which oil enters the flow pipe from the well '2,872,984 Patented Feb. 10, 1959 "ice Another object is to provide a device of this type which employs a plurality of barrel shaped collars mounted endto-end on a supporting pipe, to define a series of chambers between the pipe and the collars, the pipe and collars each having perforations communicating with said chambers.

Another object is to provide a device of this type which is well suited for economical manufacture on a quantity production basis.

Other `and more detailed objects and advantages will appear hereinafter.

In the drawings:

Figure 1 is a sectional side elevation showing a perforated pipe structure embodying my invention.

Figure 2 is a sectional elevation on an enlarged scale showing a preferred form of barrel shaped collar and the manner of mounting it on the supporting pipe.

Figure 3 shows a modified form of my invention, the barrel shaped collars being constructed of arcuate metal sections.

Figure 4 is a diagram showing the arcuate metal sections prior to assembly.

Referring to the drawings:

The central support member or pipe 10 is encircled by a plurality of barrel shaped collars 11 placed endtoend. Each of these collars 11 is provided with end portions 12 and 13 having circular openings 14 and 15, respectively, to receive the outer surface of the pipe 10. The collars 11 are preferably formed by forging them from pipe, not shown, which has a diameter equal to the largest diameter of the central portion 16. When formed in this manner the collar has wall sections which are thinnest adjacent the portion 16 and increase in thickness toward the end portions 12 and 13. The increase in thickness is such that the cross sectional area of the collar wall in any plane normal to the pipe axis is substantially the same. As indicated, additional thickness may be provided adjacent the end portions 12 by upsetting at 17. The collars 11 are placed in end-to-end abutting relationship and weld metal 18 is deposited in the V groove formed by the collar ends. This weld metal penetrates the wall of the pipe 10 so that the collars are welded to the pipe as well as to each other.

The annular chamber 19 defined between each collar and the wall of the pipe communicates through perforations 20 with the interior of the pipe 10 and through the perforations 21 to the well bore outside the collar. I prefer to place the perforations 21 in the upper tapered portion 22 of the collar which joins the center portion 16 with the end portion 12. Also, I prefer to place the perforations 20 so that they communicate with the lower portion of the chamber 19.

The lower tapered portion 23 of the collar which connects the central portion 16 with the lower end portion 13 is preferably imperforate and the outer surface 24 thereof serves to trowel Vthe mud cake 8 or other material on the wall 9 of the well bore surface. When the structure 25 including the pipe 1d and collars 11 is lowered into the well bore, these tapered surfaces 24 trowel the wall of the bore to prevent plugging of the perforations 21. The outer tapered surfaces of the collars are steeply inclined and thus the increase in diameter from one end of each collar to its mid point is only moderate. Stated in other words, the volume of each chamber is substantially less than the volume of the interior of a corresponding portion of the pipe 10.

The perforations 20 and 21 may take the form of slots or drilled holes. The particular shape of the perforation is not critical.

If desired, gravel may be introduced into each chamber 19 through an opening 26 in the collar 11 and the opening later closed by means of a suitable plug 27.

The composite structure 25 has very high crushing resistance because of the arch construction of the barrel shaped collars 11. Moreover, the tensile strength of the composite structure is very nearly uniform because of the change in wall thickness of each collar 11. Foaming of well fluid entering the interior of the pipe is minimized because the perforations Z1 are prevented from being plugged in the course of installation of the structure in the well bore and consequently the velocity of the fluid passing through perforations 21 is maintained at a reasonably low level, thereby minimizing abrasion in these perforations.

Furthermore, the perforations 20 in the wall of the pipe 10 are not subjected to contact with the mud cake, sand or other material in the well bore, and hence they provide adequate passage area to prevent high velocity of the well tluid passing through them. Accordingly, foaming and cutting are minimized at both the collar perforations 21 and the pipe perforations 20.

In the modified form of my invention shown in Figure 3, the barrel shaped collar is similar to the collar 11 previously described except that it is formed of flat stock rolled to shape. The upper section 31 is formed as a truncated cone from a flat piece. The lower section 33 is formed as an identical truncated cone from the at section 33. Axially extending welds 34 and 35 and the circumferential weld 36 hold the parts in assembled relationship. The collars 30 are mounted on the pipe 10 in the same manner as described above and are held in place by welding. The upper sections 31 are provided with perforations 32 and the lower sections 33 `serve to trowel the material on the wall surface of ythe well bore.

Removal of conventional perforated liners from wells after a period of use has been regarded as diicult, if not impossible. Conventional perforated straight pipe becomes locked in the hole after a period of use by the wedging action of mud cake, sand and other formation parts which fall from the upper portions of the bore hole into the portion where the liner is placed. Because of the reduction or elimination of sloughing in the hole and because of the high tensile strength of my composite perforated pipe structure as well as the tapered configuration of my barrel shaped members, it is anticipated that it will be possible in many cases to removev my improved device from the hole. The high strength. characteristic makes it possible to employ jars to loosen the structure and it is only necessary to move the structure through a distance equal to one-half the length of one of the barrel shaped members in order to free the structure from the walls of the well hole.

The tapering wall thickness of the barrel shaped collars results in very nearly uniform bending stiffness along the length of the pipe structure as a whole. On the other hand, providing a uniform thickness of the wall of' the collars would result in high bending stresses at the minor diameters leading to the development of yield hinges at these locations. Such yield hinges would comprise locations of high local plastic deformations or permanent set. The tapering wall thickness, from a minimum at the major diameter to maximum at the minor diameters, reduces the possibility of local yielding to a minimum.

Another advantage of my structure employing barrel shaped members is that its design encourages the building and maintaining of sand bridges in the well bore to prevent longitudinal sloughing of mud cake and forma- 4 tion material. The alternating enlargements and constrictions provided `by the series of barrel shaped members encourages sand bridging and thereby furnishes a support for the mud cake and formation materials to reduce longitudinal sloughing.

It may be desirable in some cases to eliminate the perforations 21 and 20 in the lower portion of the composite structure. For example, if one thousand feet of my composite structure were to be used in a particular well, it might be desirable to eliminate the perforations in the lowermost one hundred feet. This lower unperforated portion would serve to trowel the walls of the well bore as the structure is lowered into position, and the cost of cutting the perforations in this lower section would be eliminated. Furthermore, the composite structure, using the barrel shaped collars, may be employed without perforations in the upper portion of the well, in order to take advantage of the high resistance to crushing, and the property of reducing longitudinal sloughing.

Having fully described rny invention, it is to be understood that I do not wish to be limited to the details herein set forth but my invention is of the full scope of the appended claims.

I claim:

1. A pipe structure adapted to `be lowered into a wcll bore, comprising: a central pipe, a plurality of barrelshaped collars fixed to each other on the outer surface of the pipe in end-to-end relationship, each collar having relatively small diameter end portions and a relatively large diameter central portion therebetween, each collar cooperating with the pipe to form an annular chamber, each collar having a first tapered portion extending from the large diameter central portion to the lower end portion thereof and forming a smooth external trowelling surface for contact with the wall surface of the well, each collar having a second tapered portion extending from said central portion to the upper end portion thereof, said tapered portions providing an annular wall which is of minimum thickness at said large diameter central portion and which increases in thickness toward each end portion of the collar.

2. The device of claim 1 in which the collars are welded end-to-end.

3. The device of claim 1 in which the collars are welded end-to-end and welded to the central pipe.

4. The device of claim 1 in which the central pipe is perforated and wherein said second tapered surface of each collar is provided with perforations.

5. The device of claim 1 in which -the central pipe is perforated and wherein said first tapered portion of each collar is imperforate and said second tapered portion of cach collar is provided with perforations.

6. The device of claim 1 in which the cross-sectional area of the annular wall is substantially constant in any plane normal to the axis of the pipe.

References Cited in the tile of this patent UNITED STATES PATENTS 98,766 Harter Ian. l1, 1870 140,665 Wilson July 8, 1873 2,150,450 Maloney Mar. 14, 1939 FOREIGN PATENTS 813.005 France Feb. 15, 1937 

